strncmp

    (PHP 4, PHP 5, PHP 7, PHP 8)

    strncmp — Binary safe string comparison of the first n characters

    Description

    strncmp(string $string1, string $string2, int $length): int

    This function is similar to strcmp(), with the difference that you can specify the (upper limit of the) number of characters from each string to be used in the comparison.

    Note that this comparison is case sensitive.

    Parameters

    string1

    The first string.

    string2

    The second string.

    length

    Number of characters to use in the comparison.

    Return Values

    Returns -1 if string1 is less than string2; 1 if string1 is greater than string2, and 0 if they are equal.

    Changelog

    Version Description
    8.2.0 This function now returns -1 or 1, where it previously returned a negative or positive number.

    Examples

    Example #1 strncmp() example

    <?php

    $var1     = 'Hello John';
    $var2 = 'Hello Doe';
    if (    strncmp($var1, $var2, 5) === 0) {
    echo     'First 5 characters of $var1 and $var2 are equals in a case-sensitive string comparison';
    }
    ?>

    See Also

    • strncasecmp() - Binary safe case-insensitive string comparison of the first n characters
    • preg_match() - Perform a regular expression match
    • substr_compare() - Binary safe comparison of two strings from an offset, up to length characters
    • strcmp() - Binary safe string comparison
    • strstr() - Find the first occurrence of a string
    • substr() - Return part of a string

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    User Contributed Notes 5 notes

    up
    10
    codeguru at crazyprogrammer dot cba dot pl
    16 years ago
    I ran the following experiment to compare arrays.

    1 st - using (substr($key,0,5 == "HTTP_") & 2 nd - using (!strncmp($key, 'HTTP_', 5))

    I wanted to work out the fastest way to get the first few characters from a array

    BENCHMARK ITERATION RESULT IS:
    if (substr($key,0,5 == "HTTP_").... - 0,000481s
    if (!strncmp($key, 'HTTP_', 5)).... - 0,000405s

    strncmp() is 20% faster than substr() :D

    <?php
    // SAMPLE FUNCTION
    function strncmp_match($arr)
    {
    foreach (    $arr as $key => $val)
    {
    //if (substr($key,0,5 == "HTTP_")
    if (!strncmp($key, 'HTTP_', 5))
    {
    $out[$key] = $val;
    }
    }
    return     $out;
    }

    // EXAMPLE USE
    ?><pre><?php
    print_r    (strncmp_match($_SERVER));
    ?></pre>

    will display code like this:

    Array
    (
    [HTTP_ACCEPT] => XXX
    [HTTP_ACCEPT_LANGUAGE] => pl
    [HTTP_UA_CPU] => x64
    [HTTP_ACCEPT_ENCODING] => gzip, deflate
    [HTTP_USER_AGENT] => Mozilla/4.0
    (compatible; MSIE 7.0;
    Windows NT 5.1;
    .NET CLR 1.1.4322;
    .NET CLR 2.0.50727)
    [HTTP_HOST] => XXX.XXX.XXX.XXX
    [HTTP_CONNECTION] => Keep-Alive
    [HTTP_COOKIE] => __utma=XX;__utmz=XX.utmccn=(direct)|utmcsr=(direct)|utmcmd=(none)
    )
    up
    9
    salehrezq at gmail dot com
    7 years ago
    A note not included in the documentation:

    int strcmp ( string $str1 , string $str2 )

    Returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are equal.

    My addendum:
    If str1 and str2 are not equal, and str1 is a sub-string of str2 or vise versa. The returned int value will be negative or positive indicating how many characters the difference is between the two strings in absolute terms.

    Example:

    <?php
    $str1     = "phpaaa";
    $str2 = "php";

    echo     strcmp($str1, $str2); // 3
    ?>

    since str2 = "php" is a sub-string of str1 = "phpaaa" and "phpaaa" is greater than "php" the returned value is positive and is 3 indicating how many characters the difference is between the two strings.

    If you replace the value of str1 with str2 the result will be -3 (negative) but still indicates the absolute difference which is 3
    up
    4
    samy
    7 years ago
    I just want to highlight that (at least on php7), when testing for the existence of a string in the beginning of another string you should consider using substr or strpos (if performances is an issue).

    Here is a small benchmark (for what it's worth):
    <?php
    $n     = 'abcd';
    $l = strlen($n);
    $haystack0 = base64_encode(random_bytes(128));

    //heat
    $r = 1;
    for (    $i = 0; $i < 100000000; $i++)
    $r += $r * $r % 10000;

    //tests
    $k = 30000000;
    $res = array();
    foreach (array(    'found' => $n . $haystack0, 'not-found' => strrev($n) . $haystack0) as $f => $haystack) {
    $m = microtime(true);
    for (    $i = 0; $i < $k; $i++)
    !    strncmp($haystack, $n, $l) && $r++;
    $res["strncmp-$f"] = -$m + ($m = microtime(true));

    for (    $i = 0; $i < $k; $i++)
    (    strpos($haystack, $n) === 0) && $r++;
    $res["strpos-$f"] = -$m + ($m = microtime(true));

    for (    $i = 0; $i < $k; $i++)
    (    substr($haystack, 0, $l) === $n) && $r++;
    $res["substr-$f"] = microtime(true) - $m;
    }

    //print
    asort($res);
    print_r($res);
    echo     "\n$r"; // makes sure no auto-optimization occurs
    ?>

    This outputs:
    <?php /*
    [strpos-found] => 1.3313138484955
    [substr-not-found] => 1.4832630157471
    [substr-found] => 1.6976611614227
    [strpos-not-found] => 2.0043320655823
    [strncmp-not-found] => 2.0969619750977
    [strncmp-found] => 2.3616981506348
    */     ?>
    up
    4
    bobvin at pillars dot net
    13 years ago
    For checking matches at the beginning of a short string, strpos() is about 15% faster than strncmp().

    Here's a benchmark program to prove it:

    <?php
    $haystack     = "abcdefghijklmnopqrstuvwxyz";
    $needles = array('abc', 'xyz', '123');
    foreach (    $needles as $needle) {
    $times['strncmp'][$needle] = -microtime(true);
    for (    $i = 0; $i < 1000000; $i++) {
    $result = strncmp($haystack, $needle, 3) === 0;
    }
    $times['strncmp'][$needle] += microtime(true);
    }
    foreach (    $needles as $needle) {
    $times['strpos'][$needle] = -microtime(true);
    for (    $i = 0; $i < 1000000; $i++) {
    $result = strpos($haystack, $needle) === 0;
    }
    $times['strpos'][$needle] += microtime(true);
    }
    var_export($times);
    ?>
    up
    4
    elloromtz at gmail dot com
    14 years ago
    if length is 0 regardless what the two strings are, it will return 0

    <?php
    strncmp    ("xybc","a3234",0); // 0
    strncmp("blah123","hohoho", 0); //0
    ?>
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